Braun electric toothbrush charging

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The Braun Triumph 3738 toothbrush and 3731 charger use an inductive
coupling arrangement to charge the toothbrush battery.  Right now
SWMBO's unit isn't charging and I'm tasked with fixing it.  Does
anyone know if this operates at line frequency or something higher?
(That will help sensing the field from the charging base to verify it
is operational before I disassemble the toothbrush itself.)

Re: Braun electric toothbrush charging
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It's an air-cored transformer in its simplest form, with absolutely no  
"smarts" in the base unit - meaning you'll have 50Hz emanating from the  
base.

Whereas with most battery-powered devices you expect the charge to gradually  
diminish, with these units the base unit usually fails long before the  
battery starts deteriorating. Almost invariably, the coil in the base goes  
open-circuit.

Good luck in getting the base open (my one attempt revealed liberal use of  
epoxy), and when (or rather, if) you do, good luck in re-winding the coil.  
Given the time of year, you might just want to kill the proverbial pair of  
birds by buying her a new one - it'll be far less hassle.

--  
Bob Milutinovic
Cognicom


Re: Braun electric toothbrush charging
On Fri, 13 Dec 2013 22:15:19 +1100, "Bob Milutinovic"

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Thanks for the quick reply, Bob.  I realised it was an air-cored
transformer, but I allowed for the possibility that they were
operating at a higher frequency to get decent coupling efficiency.  I
was still out looking for an AM portable to check if there was any
50Hz field around the base unit.

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Given the 2W nameplate rating, that's a pretty high Zin - about 300K
if resistive.  Some coil, so presumably a blocking cap to help keep
the current half-decent.  There goes the prospect of measuring for an
O/C coil without cracking the case ....

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This one has the cord end of the wall unit seemingly retained in the
case with visible barbs on opposite sides of the case.  They resist
decent efforts to depress them though.

If there is bugger-all of consequence in that wall unit, the only
reason for the size is as a handle for the tri-lobe tool moulded
thereon which undoes the toothbrush base.

Re: Braun electric toothbrush charging
On Fri, 13 Dec 2013 22:15:19 +1100, "Bob Milutinovic"

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Making sure we are using the same terms here:  Wall unit = the flat
plug-into-the-outlet piece.  Base is the coil assembly that the
toothbrush sits atop to be charged.  Toothbrush = obvious.

I have a "search coil" of ~130 turns of 0.7mm wire on a bobbin.
Bobbin ID is 15mm and coil OD is 31mm.

Test #1:  With the coil (unterminated) connected to the 15MHz CRO,
absolutely zilch on max sensitivity when the coil is sitting flat atop
the energised base.  Definite flatliner.

Test#2:  Fed an AC current of 1A through the coil and brought the
toothbrush right up to sitting on the bobbin.  No interest whatsoever
on the battery status/charge LCD.  I have forgotten all my inductor
stuff way back, but if the factory base has an input (label) of 2W
then this may well have had a comparable field give or take the odd
order of magnitude.

Just to be sure we are talking about the same product.  The previous
generation product had a base-cum-storage-tower construction and the
base had a keyed spigot for locating the toothbrush with the charge
LED outwards.  The one we have has an egg-shaped hole through the base
with a matching shape on the bottom of the toothbrush.  The video of
battery replacement (link in my reply to Andy) shows the toothbrush
under discussion.

Re: Braun electric toothbrush charging
I use both Braun and Sonicare toothbrushes. (I like variety.) The Brauns  
charge fine on the Sonicare base (though they just "sit there", without even a  
nub to hold them in place).

I have a few extra Sonicare chargers. I will gladly send one to any US  
resident who needs one, for the cost of postage, plus 50 cents handling.  


Re: Braun electric toothbrush charging
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Right you are; it was the previous generation which I had, in which the base  
was barely more than a small plastic disc and a nub-encrusted protrusion  
with which the brush docked.

This morning I had a look at my daughter's newer unit, which has a slightly  
wedge-shaped oval as the docking point, and that seems to have considerably  
more bulk to the base unit - about an inch tall - which may likely house  
additional electronics.

I still contend though that because of the relatively low price of these  
units, it's not worth pursuing repair for any reason other than personal  
satisfaction.

--  
Bob Milutinovic
Cognicom


Re: Braun electric toothbrush charging
I goofed somewhat. I have a couple of spare Braun chargers, as well. The offer  
stands.  


Re: Braun electric toothbrush charging
On Mon, 16 Dec 2013 04:09:35 -0800, "William Sommerwerck"

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The offer is appreciated but as I'm "down under" and it would require
an adaptor to connect to our AU/NZ outlet, it's probably easier to
bite the bullet and purchase the replacement from the Braun guys.

Re: Braun electric toothbrush charging
On Mon, 16 Dec 2013 18:47:33 +1100, "Bob Milutinovic"

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The one we have is like this (but with Oz-pins of course ...):

http://www.service.braun.com/product/big_img.asp?artGrp37%31&partno00%67040173&l=GB&c=AU&pic=parts |xl|67040173_xl.jpg

Sorry about the URL mess.

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That's the current Plan A.  $34 plus $10 shipping from east coast, or
$39.95 ex the one local source.

Then I can do a Jeff Liebermann learn-by-destroying job on the
existing wall unit.  Wedging a couple of flat-blades into the current
one showed what appeared to be the end of a pcb and clear silicon bog
filling the entire enclosure.  There's something in there warranting a
pcb, and enquiring minds (this one at least) feel a need to know.

Re: Braun electric toothbrush charging
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Well that's an entirely different kettle of fish; the ones I've seen have  
the male mating on the base.

This is my daughter's charging base looks like; mine was similar but much  
thinner -
http://www.thepartsbiz.com/assets/images/84848387b.jpg

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Indeed, indeed. But just as I discovered when going through a similar  
procedure with a top-of-the-range Philips shaver in which the batteries had  
leaked (gotta love the old NiCd technology!), you'll likely find that the  
sum of the parts is worth a tenth of what they want for it.

--  
Bob Milutinovic
Cognicom


Re: Braun electric toothbrush charging


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But all the people who test-shaved the guineapigs have to get paid too.

--  

beslutning at undlade det.



Re: Braun electric toothbrush charging
On Tue, 17 Dec 2013 17:00:20 +1100, "Bob Milutinovic"

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SWMBO's previous one(s) were like that style.

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If they can sell it in Oz for $34 then its probably $2 tops to the
Chinese factory.  That may buy all the parts (labour being
inconsequential there, a bowl of rice per week) in their market but
isn't going to dent the parts list here.

Opening is for learning only.  Not sure what I will find - electronics
failed or the coil O/C.

Re: Braun electric toothbrush charging
On 13/12/2013 10:20, pedro wrote:
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With an OralB charger base,DVM Fluke 77 and 1mH small choke near the  
spigot of the base ,
measured 0.45V ac, HF not mains frequency but Fluke still registered  
something

Re: Braun electric toothbrush charging
I would check the coil in the hand piece.  Either try a different base or  
open by twisting. The hand piece coil is accessible.  I fixed one that had  
opened and needed resoldering.

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Re: Braun electric toothbrush charging
pedro wrote:

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The old ones (no idea what model #) have a simple charging circuit
of a diode and a coil in the bottom of the handle, and 2 Ni-Cd
batteries.  I can't get that size battery anymore, so I rigged two
larger cells outside and taped to the handle.  It has worked
for some time.  I used to replace the cells every 2-3 years when
the wouldn't hold charge anymore.

Jon

Re: Braun electric toothbrush charging

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The techo guy at the authorised Braun service centre tested my charger
and confirmed it was dead as, so I purchased a replacement.  He also
asserted that they do not contain any smarts, and operate at line
frequency.

For the benefit of others who may find themselves in this position,
the charger coil is driven at 72kHz unloaded, and this rises to 76kHz
when charging the toothbrush.  So much for line frequency!

When I get a round tuit I may attack the dead unit with the trusty
Dremel to see what exactly is inside.

Thanks for all comments/suggestions.

Re: Braun electric toothbrush charging
On 18/12/2013 15:23, pedro wrote:
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See this EEVBLOG for insides of Braun toothbrushes. It is not line  
frequency.

http://www.youtube.com/watch?v=JJgKfTW53uo


Chris

Re: Braun electric toothbrush charging
On Sat, 21 Dec 2013 15:11:33 +1100, Chris Jones

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In case you hadn't noticed (in the post you replied to... ), I had
advised that very fact.

The one David is checking out is quite a different model, and in my
case the charger was u/s which made the initial determination of
frequency impossible.

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